1. Field of the Invention
This invention relates to a method and an apparatus for laser analysis of dioxins, adapted to analyze dioxins, which are contained in a gas such as an exhaust gas or water such as waste water, in real time. More specifically, the invention relates to a dioxins analyzer for directly analyzing dioxins in an exhaust gas, which is discharged from an incinerator, a thermal decomposition furnace, or a melting furnace, such as a municipal solid waste incinerator, an industrial waste incinerator, or a sludge incinerator, in real time without a time delay; a combustion control system for controlling combustion in the furnace based on the results of analysis by the analyzer; and a dioxins analysis method and a dioxins analyzer for measuring the concentration of a hazardous substance such as an organohalogen compound in seepage water from a dumping site or industrial waste water, and a waste water treatment system using the analysis method or analyzer.
2. Description of the Related Art
Dioxin has high toxicity in a tiny amount, and development of a high sensitivity method for its analysis is desired. Thus, the application of a laser analysis method capable of high sensitivity analysis has been worked out. In recent years, a proposal has been made that a combination of supersonic jet spectroscopy and resonance enhanced multiphoton ionization can measure the spectra of chlorine substituted compounds which belong to dioxins (C. Weickhardt, R. Zimmermann, U. Bosel, E. W. Schlag, Papid Commun, Mass Spectron, 7, 198(1993)).
However, the above proposal concerns a method for analyzing a gas, which ejects a gas sample as a jet in a vacuum and cools it instantaneously to a temperature close to absolute zero point, thereby simplifying its spectrum. The detection limit of this method for dioxin and its derivatives (hereinafter referred to as xe2x80x9cdioxinsxe2x80x9d) is about ppb, and 5- to 6-digit concentration of the sample is necessary for the actual analysis of dioxin. As noted from this, the method takes a great deal of time and effort for detection.
The conventional manual analysis takes 1 to 2 months until the results of analysis are obtained. Thus, it is difficult to measure dioxins generated in the incinerator daily, and control combustion, as necessary, to perform an operation always fulfilling the proper regulatory value.
Furthermore, the above-mentioned method for analysis of dioxins uses laser light of a pulse width of the order of nanoseconds (10xe2x88x929 second) for selective ionization. As the number of the chlorine atoms increases, intersystem crossing into a triplet system occurs because of a so-called heavy atom effect, shortening the life of excitation. Consequently, no ion signals are observed.
A method for detecting sample molecules, which comprises irradiating sample molecules with laser light to ionize them selectively, was proposed (see Japanese Unexamined Patent Publication No. 222181/1996) . When the sample molecules are selectively ionized, only the targeted sample can be detected, and the current homologues of dioxins in the exhaust gas cannot be analyzed in real time. Moreover, nanosecond laser light with a satisfactory detection sensitivity is used in selective ionization. In this case, however, real-time analysis of dioxins is impossible, as stated earlier. According to the proposed method, only one particular isomer can be measured. When measuring other substances, wavelength scanning is necessary. In making measurements while scanning wavelengths, adjustment for varying wavelengths needs to be made for each measurement. The adjustment takes so much time that homologues of dioxins in the exhaust gas cannot be analyzed in real time. According to the proposal, moreover, selective ionization may result in the failure to show detection peaks, if the wavelength varies only by several picometers (pm). Thus, constant correction of wavelength is necessary. In detecting dioxins at a location adjacent to the incinerator in actual operation, extensive damping means is needed for preventing vibrations, and measurement of dioxins is interrupted at each wavelength correction.
It has also been proposed to estimate the concentration of dioxins by measuring the concentration of CO, and control combustion in an incinerator or the like based on the estimates. When the CO concentration is as high as 100 ppm, there confirms to be a correlation between the CO concentration and the dioxins concentration. As shown in FIG. 14, however, no correlation holds between the dioxins concentration and the CO concentration in a region in which the CO concentration is as low as 50 ppm or less. Thus, measurement of the CO concentration alone is not sufficient for effective control of combustion which can prevent the occurrence of dioxins. Recent years have seen the establishment of combustion control at low CO concentrations. Consequently, there is a demand for reliable prevention of dioxins occurrence by direct instantaneous measurement of dioxins.
Decomposition products of dioxins, such as chlorobenzene (CB) and dichlorobenzene (DCB), have been considered to be correlated to dioxins in terms of concentration. The measurement of these decomposition products or dioxins precursors is not direct measurement of dioxins, and cannot lead to strict evaluation of the state in the incinerator. Thus, real-time analysis of the exhaust gas is demanded, and the utilization of the results of analysis for combustion control is desired. In detail, it has been impossible to evaluate whether decreases in the decomposition products of dioxins mean that the occurrence of dioxins has been suppressed, or the decomposition of dioxins has been suppressed, although dioxins are occurring.
In measuring a substance whose concentration correlates to the concentration of dioxins, one particular substance is measured in selective ionization, as described previously. If dioxins cannot be detected, despite their actual occurrence, because of other factors, such as displacement of the optical axis of laser light and clogging of sampling piping, the concentration of dioxins cannot be measured properly. To dissolve this drawback, it is necessary to provide two measuring devices and conduct analysis while monitoring the data obtained. In this case, an extensive analyzer is required.
Conventionally, soil water, such as seepage water from a dumping site or industrial waste water, is placed in an adjustment tank, where its amount and pH are adjusted. Then, the adjusted soil water is rid of organic matter and nitrogen components in a bioremediation tank, and coagulated with the addition of a coagulant in a coagulation-sedimentation tank to separate heavy metals and suspended solids (SS). Then, the supernatant is subjected to accelerated oxidation to decompose difficultly decomposable organic substances contained therein, including dioxins. Then, the oxidized liquid is passed through a sand filtration tower and an activated carbon adsorption tower, and then discharged as treated water. A proposal for purification of water containing dioxins, the difficultly decomposable organic substances, is a method which comprises adding hydrogen peroxide to water containing organochlorine compounds, and applying ultraviolet radiation to decompose the compounds. A method for decomposing dioxins by introducing ozone instead of irradiation with ultraviolet radiation has also been proposed.
According to the conventional methods, analysis of dioxins has been carried out, with concentration from waste water being repeated with the use of an organic solvent. Usually, a long time of more than 70 hours has been taken, making rapid measurement difficult. To decrease the dioxins concentration in the waste water, application of ultraviolet rays or injection of much ozone, as described above, has been performed. Measurement responsive to the concentration of dioxins in waste water is still difficult, and decomposition of the dioxins in the presence of an excess of ultraviolet radiation or ozone is common practice. Thus, a demand is made for decomposition adapted for the concentration of hazardous substances in waste water, including dioxins.
The present invention has been accomplished in light of the foregoing problems with the earlier technologies. The object of the invention is to provide a method and an apparatus for laser analysis of dioxins, which can make real-time analysis of dioxins contained in a gas such as an exhaust gas or water such as waste water.
An aspect of the present invention is a dioxins analyzer for applying laser light to a gas or solution containing dioxins to perform laser multiphoton ionization of the dioxins, and then measuring the ionized dioxins.
Thus, the analysis of dioxins can be conducted in real time.
Another aspect of the invention is a dioxins analyzer, comprising:
sampling means for directly sampling a combustion gas containing dioxins in an exhaust gas discharged from an incinerator, a thermal decomposition furnace, or a melting furnace;
ejection means for ejecting the sampled gas containing the dioxins into a vacuum chamber with the use of a nozzle having a pulse valve for forming a supersonic jet;
laser applicator means for applying laser light of a broad spectral width into the ejected supersonic jet to form molecular ions of homologues of the dioxins during a resonance enhanced ionization process; and
a time-of-flight mass spectrometer for analyzing the resulting molecular ions for dioxins, and wherein:
the homologues of the dioxins in the combustion gas are directly analyzed.
This aspect eliminates the burden of measuring the concentration of an alternative to dioxins, such as CO, and analyzing the dioxins based on the correlation between the concentration of the alternative and the concentration of dioxins. Homologues of dioxins in the combustion gas can be analyzed directly. Unlike selective ionization, tiresome adjustment of wavelength is unnecessary, and simple analysis permits high sensitivity analysis of dioxins.
The laser light of the broad spectral width may be laser light of a pulse width shorter than a life in an electron excited state of molecules to be measured.
According to this constitution, homologues of dioxins can be analyzed simultaneously.
The laser light may be femtosecond laser light of 2 to 500 femtoseconds.
According to this constitution, homologues of dioxins can be analyzed simultaneously.
The wavelength of the laser light may be a fixed wavelength in a range of 240 to 350 nm.
According to this constitution, homologues of dioxins can be analyzed simultaneously.
The ejection means may have the pulse valve for ejecting the sampled gas in a direction coaxial with a flying direction of the ions, and the laser light may be applied from a direction perpendicular to the jet ejected from the pulse valve.
According to this constitution, all the ions ionized from dioxins in the ejected sampled gas can be detected with an ion detector.
The nozzle of the ejection means may be a slit nozzle.
According to this constitution, the ejected gas can be shaped in a rectangular form, and a further increase in the detection sensitivity can be achieved.
The sampling means may be a sampling pipe equipped with a filter for removing ash in the exhaust gas.
According to this constitution, clogging in the sampling pipe can be prevented.
The sampling means may include backwashing means.
According to this constitution, if clogging occurs, the clogged sampling pipe can be immediately washed, and analysis is not interrupted.
A front end of the sampling means may be provided in at least one location inside the incinerator, thermal decomposition furnace or melting furnace, or inside an exhaust gas flue.
According to this constitution, the site of analysis of dioxins can be set as desired.
The time-of-flight mass spectrometer may be a reflectron type mass spectrometer.
This constitution improves the sensitivity of analysis.
Another aspect of the invention is a dioxins analysis method, comprising:
multiphoton ionizing dioxins in an exhaust gas or waste water with the use of laser light, the exhaust gas being discharged from an incinerator, a thermal decomposition furnace, or a melting furnace; and
analyzing homologues of the dioxins simultaneously.
According to this aspect, homologues of dioxins can be analyzed simultaneously.
The laser light of a broad spectral width may be femtosecond laser light of 2 to 500 femtoseconds.
According to this constitution, homologues of dioxins can be analyzed simultaneously.
Another aspect of the invention is a first combustion control system in an incinerator for charging a combustible material into an incinerator, a thermal decomposition furnace, or a melting furnace, maintaining an amount of heat generated by combustion at a constant level, and suppressing occurrence of a hazardous gas containing dioxins, comprising:
the aforementioned dioxins analyzer capable of instantaneously measuring the dioxins in an exhaust gas from the incinerator, thermal decomposition furnace, or melting furnace; and
combustion air control means,
whereby a concentration of the dioxins is detected without a time delay, and an amount of combustion air is varied according to the concentration of the dioxins detected.
According to this aspect, combustion preventing the occurrence of dioxins can be performed.
In the combustion control system, the combustion air control means may control an amount of air and a concentration of oxygen of one or both of primary combustion air and secondary combustion air.
According to this constitution, combustion without the occurrence of dioxins according to the status of combustion can be performed.
Another aspect of the invention is a second combustion control system in an incinerator for charging a combustible material into an incinerator, a thermal decomposition furnace, or a melting furnace, maintaining an amount of heat generated by combustion at a constant level, and suppressing occurrence of a hazardous gas containing dioxins, comprising:
the above dioxins analyzer capable of instantaneously measuring the dioxins in an exhaust gas from the incinerator, thermal decomposition furnace, or melting furnace; and
dust collection/removal means for removing dust in the exhaust gas,
whereby a concentration of the dioxins is detected without a time delay, and an amount of spray of an adsorbent for adsorbing the dioxins is varied according to the concentration of the dioxins detected.
According to this aspect, the adsorbent can be sprayed as required, and can be controlled to an appropriate spray amount.
Another aspect of the invention is a third combustion control system in an incinerator for charging a combustible material into an incinerator, a thermal decomposition furnace, or a melting furnace, maintaining an amount of heat generated by combustion at a constant level, and suppressing occurrence of a hazardous gas containing dioxins, comprising:
the above dioxins analyzer capable of instantaneously measuring the dioxins in an exhaust gas from the incinerator, thermal decomposition furnace, or melting furnace;
combustion air control means; and
dust collection/removal means for removing dust in the exhaust gas,
whereby a concentration of the dioxins is detected without a time delay, an amount of combustion air is varied according to the concentration of the dioxins detected, and an amount of spray of an adsorbent for adsorbing the dioxins is varied according to the concentration of the dioxins detected.
According to this aspect, efficient combustion preventing the occurrence of dioxins can be performed, and also the adsorbent can be sprayed as required, and can be controlled to an appropriate spray amount.
Another aspect of the invention is a fourth combustion control system in an incinerator for charging a combustible material into an incinerator, a thermal decomposition furnace, or a melting furnace, maintaining an amount of heat generated by combustion at a constant level, and suppressing occurrence of a hazardous gas containing dioxins, comprising:
the above dioxins analyzer capable of instantaneously measuring the dioxins in an exhaust gas from the incinerator, thermal decomposition furnace, or melting furnace; and
a stabilizing burner,
whereby a concentration of the dioxins is detected without a time delay, and a supporting gas is fed into the exhaust gas according to the concentration of the dioxins detected to burn the dioxins in the exhaust gas.
According to this aspect, discharge of dioxins to the atmosphere can be suppressed.
Another aspect of the invention is a fifth combustion control system in an incinerator for charging a combustible material into an incinerator, a thermal decomposition furnace, or a melting furnace, maintaining an amount of heat generated by combustion at a constant level, and suppressing occurrence of a hazardous gas containing dioxins, comprising:
the above dioxins analyzer capable of instantaneously measuring the dioxins in an exhaust gas from the incinerator, thermal decomposition furnace, or melting furnace;
combustion air control means; and
a stabilizing burner,
whereby a concentration of the dioxins is detected without a time delay, an amount of combustion air is varied according to the concentration of the dioxins detected, and a supporting gas is fed into the exhaust gas according to the concentration of the dioxins detected to burn the dioxins in the exhaust gas.
According to this aspect, efficient combustion preventing the occurrence of dioxins can be performed, and discharge of dioxins to the atmosphere can be suppressed even if resynthesis of dioxins in the flue takes place.
The dioxins analysis method may comprise:
applying laser light to a surface of a solution to be measured to perform laser multiphoton ionization of dioxins on the surface; and
determining a concentration of the dioxins in the solution to be measured.
In the dioxins analysis method, the laser light may be nanosecond laser light or femtosecond laser light.
In the dioxins analysis method, the laser light may be laser light of a wavelength of 300 nm or less.
The aforementioned dioxins analyzer may comprise:
a laser device for applying laser light to a surface of a solution, which is to be measured, in a reservoir;
a counter electrode provided opposite the surface of the solution, which is to be measured, in the reservoir;
a high voltage power source for applying a high voltage between the counter electrode and the reservoir; and
a processor for amplifying and processing an electric current signal obtained.
In the dioxins analyzer, an incidence angle of the laser light applied to the surface of the solution to be measured may be 15 degrees or less.
In the dioxins analyzer, the laser light may be nanosecond laser light or femtosecond laser light.
In the dioxins analyzer, the wavelength of the laser light may be a fixed wavelength in a range of 240 to 300 nm.
Another aspect of the invention is a waste water treatment system for decomposing difficultly decomposable substances in waste water, including:
the dioxins analyzer of the invention capable of measuring a concentration of dioxins in the waste water, and wherein:
the concentration of the dioxins is detected without a time delay, and the dioxins in the waste water are decomposed in the presence of hydroxyl radicals according to the detected concentration of the dioxins.